Spring的Ioc模拟实现详细介绍

public Class ServiceImpl{
  @Autowired
   Dao dao;
   
  public void getData(){
    dao.getData();
  }

public interface IocDao {
  public void sayhello(); //一个用来测试的接口
}

public class IocDaoImpl implements IocDao {
  @Override
  public void sayhello() {
    // TODO Auto-generated method stub
    System.out.println("hello word");//实现我们的dao接口里的方法
  }
}

public interface IocDaoService {
  public void sayhello();//业务类接口,这里就跟dao一样
}

public class IocDaoServiceImpl implements IocDaoService {
  private IocDao iocDao;  //创建一个接口.
  public IocDao getIocDao() {
    return iocDao;
  }
  //编写IocDao接口对应的set方法用于依赖注入
  //依赖注入的方式有三种：接口注入，构造方法注入，set注入;
  //此处为set注入
  public void setIocDao(IocDao iocDao) {
    this.iocDao = iocDao;
  }
  @Override
  public void sayhello() {
    // TODO Auto-generated method stub
    iocDao.sayhello();//调用接口方法
  }
}

<beans>
 <bean id="i" class="com.hck.dao.impl.IocDaoImpl"/> 
 <bean id="iocService" class="com.hck.service.impl.IocDaoServiceImpl">
   <property name="iocDao" ref="i"></property>
 </bean> 
</beans>

//模拟ClassPathXmlApplicationContext实现的一个接口BeanFactory
public interface BeanFactory {
  public Object getBean(String beanName);
}

//模拟ClassPathXmlApplicationContext去读取配置文件
public class ClassPathXmlApplicationContext implements BeanFactory {
  //定义map集合来存放bean.xml里的bean的id跟其对应的实例化对象
  //<bean id="i" class="com.hck.dao.impl.IocDaoImpl"/> 
  //那么类似的存放bean.put("i",new IocDaoImpl());这样子.
  Map<String, Object> beans=new HashMap<String,Object>();
  public ClassPathXmlApplicationContext(String xmlPath){
      try {
        //创建SAXBuilder对象解析文档
        SAXBuilder saxBuilder = new SAXBuilder();
        //解析build里的参数是一个文件路径.
        Document document = saxBuilder.build(xmlPath);
        //document.getRootElement().getChildren("bean")获取所有<bean>标签内容
        List elements = document.getRootElement().getChildren("bean");
        //遍历<bean>对象
        for (int i = 0; i < elements.size(); i++) {
          //获取第一个<bean>标签elements.get(0);
          Element element = (Element) elements.get(i);
          //获取<bean>标签里的<id>属性，
          //<bean id="i" class="com.hck.dao.impl.IocDaoImpl"/> 
          //即String beanName="i";
          String beanName = element.getAttributeValue("id");
          //同上String clazz="com.hck.dao.impl.IocDaoImpl";
          String clazz = element.getAttributeValue("class");
          //加载类对象并且实例化.Object object=new IocDaoImpl();
          Object object = Class.forName(clazz).newInstance();//object是IocDaoServiceImpl
          //将他们添加在map集合里,后面可以根据beanName直接获取到实例化对象.
          beans.put(beanName, object);
          //遍历<bean>标签下的<property>字标签.
          //第一个标签没有字标签所以直接跳过.已第二个为例子
          //<bean id="iocService" class="com.hck.service.impl.IocDaoServiceImpl">
          //<property name="iocDao" ref="i"></property></bean>
          List elements2 = element.getChildren("property");
          for (int j = 0; j < elements2.size(); j++) {
            //此处我们将获得<property name="iocDao" ref="i"></property></bean>
            Element element2 = (Element) elements2.get(j);
            //相当于String propertyName="iocDao";
            String propertyName = element2.getAttributeValue("name");
            //相当于String refBean="i";
            String refBean = element2.getAttributeValue("ref");
            //相当于String propertyName="IocDao";
            //目的是为了得到一个方法的名字setIocDao,用于反射调用
            propertyName = propertyName.substring(0, 1).toUpperCase() + propertyName.substring(1);
            //这里的methodName="setIocDao";
            String methodName = "set" + propertyName;
            //获取Map集合里Key="i"的值;i对应的是IocDaoImpl的实例化对象
            //相当于 Object object2 =IocDaoImpl;
            Object object2 = beans.get(refBean);
            //获取IocDaoServiceImpl方法里的setIocDao方法.
            //第一个方法是方法名，第二个参数是方法的参数类型.
            Method method = object.getClass().getDeclaredMethod(methodName,
                object2.getClass().getInterfaces());
            //调用方法，并传入参数，完成依赖注入.
            method.invoke(object, object2);
          }
        }
        //      String beanName=document.getElementById(id).attributes().get("class");
        //      Object object=Class.forName(beanName).newInstance();
        //      return object;
      } catch (Exception e) {
        e.printStackTrace();
        // TODO: handle exception
      }
  }
/* (non-Javadoc)
 * @see com.hck.ioc.BeanFactory#getBean()
 */
@Override
public Object getBean(String beanName) {
  // TODO Auto-generated method stub
  return beans.get(beanName);
}  
}

public class Ioc {
  public static void main(String[] args) {
  ClassPathXmlApplicationContext applicationContext=new ClassPathXmlApplicationContext("src/bean.xml");
  IocDaoService ids=(IocDaoService)applicationContext.getBean("iocService");
  ids.sayhello();
}
}

hello word